Transmitter receiver duplexing circuit for radar apparatus



Nov. 6; 1951 A. J. oRTUsl ErAL TRANSMITTER RECEIVER DUPLEXING CIRCUI'FOR RADAR APPARATUS 2 SHEETS- SHEET 1 Filed Jn. 17,

IST RECEIVER ATTORNEY A. J. oRTUsl Erm.v 2,574,055 TRANSMITTER RECEIVERDUPLEXING CIRCUIT RoR RADAR APPARATUS 2 SHEETS-SHEET 2 Nov. 6, 1951Filed Jan; 17. 1949 #w25/vroeg A/WO/A/f JfA/V @Rn/.s4 PA 7570.6"FFC/901467?, fr z.

` A rrZR/vs y Patented Nov. 6, 1951 TRANSMITTER RECEIVER DUPLEXINGCIRCUIT FOR RADAR APPARATUS Antoine Jean Ortusi and Patrice Fechner,Paris, France, assignors `to Compagnie Generale de Telegraphie Sans Fil,a corporation of France Application January 17, 1949, Serial No. 71,263In France February 4, 1948 (Cl. Z50-13) 2 Claims.

The present invention relates to an improvements in the device describedin the patent application filed on July 19, 1946, in the United States,Serial No. 684,820, entitled: Improvements in or relating to a method ofand means for the radio-electric detection of obstacles, in which asingle antenna was used for transmitting and receiving high frequencysignals in a radiolocation system, said antenna being supplied by twodifferent guides, one of which was connected to the transmitter, theother to the receiver. With each of said two guides was associated avariable tuning resonator, each of which formed a reactance thattransferred a variable impedance to each of said guides, one of saidresonators being intended to protect the receiver during thetransmission of a signal, the other to isolate the transmitter duringthe reception of the echo.

The present invention has for its object an improved embodiment of thisdual protecting system, wherein use is made of a single variablereactance to render simultaneously, either the receiver-guidenon-conducting and the transmitter-guide conducting, or to obtain theconverse result, said variable reactance being located outside these twoguides. stallation is simplified and the operation thereof is made moreconvenient and moreover becomes more reliable.

According to the invention, said reactance, which is adapted to varyproportionally to one of its parameters, in particular to its voltage,is connected to both the transmitter and receiver guides by cables, inparticular coaxial cables, the lengths of which are so calculated thatthe impedance transferred to one of the two guides is zero, and theimpedance transferred to the other.

guide is infinite, means being provided for automatically varying saidparameter in such a manner as to reverse these conditions.

According to a form of embodiment of the invention, said variablereactance comprises a magnetron, the anode voltage of which is made tovary.

The invention also applies to any device for regulating the distributionof the power from a single ,channel between two U. I-I. F. channels, itsbeing possible for this regulation to be sudden (triggered off or on) orgradual. It also applies to the converse arrangement which is adapted tofeed successively into a common channel, the ultra-high frequencysignals from two separate supply channels.

The inventionwill be more clearly understood by means of theaccompanying gures which show,

In this manner the inby way of non-limitative examples, a number ofembodiments thereof.

Fig. 1 shows a curve that gives the value of the coeiiicient oftransmission in a guide as a function of the length of the coaxial cableconnecting a magnetron to said guide;

Fig. 2 shows a diagram of the principle of the invention;

Fig. 3 shows a form of embodiment of the invention as applied to atransmitter-receiver device using a single antenna; and

Fig. 4 shows a diagrammatic view of the embodiment relating to a devicefor regulating the distribution of the power between two U. H. F.channels.

In the French patent application for Improvements in the methods andapparatus for modulating ultra-short Waves, filed by the CompagnieGenerale de Telegraphie Sans Fil, on` February 6, 1945, it was observedthat when a magnetron is connected to a guide by means of a coaxialcable, said magnetron transfers to the guide an impedance that varies,on the one hand with the length of the coaxial cable, and on the otherhand with the voltage supplied between the electrodes of the magnetron.If the anode voltage of the magnetron is allowed to remain at zero, Fig.1 shows the variations of the coecient of transmission T in the guide asa function. of the length l of the coaxial cable. When the length of thecoaxial cable is Z1, the transferred impedance in the guide is infinite,and the transmission is effected completely; when the length of saidcable is Z2, the transferred impedance in the guide is zero and thetransmission is stopped. Between two successive maximums, the length lvaries half a wave-length, Z1 and l2 being approximately equal to(2n-|-l) \/4 and respectively wherein n is an integer and i thewavelength.

Fig. 2 represents the diagram of principle that shows how the foregoingdiscovery has been used for carrying out the invention. In this figure,G1 and G2 represent two rectangular wave-guides, each of which isterminated by its characteristic impedance Ze and Zc respectively. Amagnetron M is connected to said guides by means of two coaxial cablesC1, C2 that lead to a common coaxial cable C which is coupled to themagnetron by means of the loop b. The coaxial cables C1 and C2 terminatein two loops b1 and b2, the plane In such a device, the values of thelengths Z1 andl l2 correspond to those of Figure 1 i. e.

l.: (211+ 1mi and 12:@

so that when the anode voltage of the magnetron M is zero, the guide G2is non-conducting,v the guide G1 effects the transmission of the wave,as shown by the arrows in continuous lines and the devices I1 and Iz, I1having its pointer opposite the maximum value and I2 its pointer.` at.

zero. If a predetermined voltage V is supplied 'to themagnetrom theimpedance transferred to each of the two guides Will be varied and it isonly necessary suitably to adjust the value of V in.order to reverse theconditionsv of operation, i. e..to-render Athe guide G1 non-conductingand the guide G2 conducting, as shown by the arrows in dotted lines andthe devices I1 and I2, I1 having its pointer on zero and I2 its pointeroppositethe maximum value. Such an operation is tantamount to assumingthat the operation of each of the two guides alternately correspondstothe-points AandB-ofthe curve-of Fig. 1.

'The embodiment-shownin Fig, 3., which relates to atransmitter-receiverV device using a single antenna, will now beconsidered. This iigure shows, at GE. the transmitter Vguide and at GRthe receiver guide, both leadingto the guide that acts: as an antennaA1, terminating in its characteristic impedance Z5. At M is shown themagnetronv which is adapted to render the two guides alternatelynon-conducting and: conducting by means of thecoaxialfcables C, C1, C2.The lengths l and Z are adjusted as-hereinbefore indicated. At DC is-vshown the control deviceY that produces the voltage pulses shownsymbolically at i; said pulsesare transmitted on the one hand tothe-electrode lc of the magnetron G which generates U. H. F.transmission signals and which isv thus renderedconducting andtransmitsa, signal, and onfthe other hand' to" the electrode K f the magnetron Mwhich is likewise thus rendered .conducting by means of the adjustingdevice RE. During the transmission of this signaLthe wave passes throughthe guide GE while the guide GR is on the contrarywrenderednonconducting. During the period of time that elapses between thesignal' and the next signal the reverse effect occurs: GE is madenon-conducting and GR conducting. The source S of direct current voltagesupplies a positive direct current voltage to both 'lthe guides and boththe anodes A, a. of the twoV magnetrons,.and P1, P2 are pistons foradjusting the two guides. R de.- notes. the receiving` device. The arrowin continuous linesrepresents the wave transmitted, andthe other arrowin dotted lines represents the echo received.

Finally, Fig. 4' shows a diagrammatic view Yof the modification whereinthe U. H. F. power that enters theV guide G is distributed between theguides G1 and G2, each of which is terminated by a lreceivingl deviceR1, R2, The same lreference numeralsv designate-the same-elements as inthe previous figures. The adjustment of this distribution can, atwillgbe effectedabruptlyor, on

the contrary, in a gradual manner. For the sake of simplicity, thecomplete adjusting circuit, which is the same as that of Fig. 3, has notbeen shown.

The device according to the invention has numerous advantages as4-compared with the dual protection system commonly used in radarapparatus and more commonly called T R (transmitter-receiver), such asystem comprising two ionization tubes, one of which is associated withthe transmitter guide and the other with the receiver'guide and whichsuccessively render said guides non-conducting and conducting bybecoming ionized by the effect of the transmitted wave or of thereflected wave. The device according to the invention, in addition tothe fact that it eliminates the use of these expensive and fragiletubes, uses a single magnetron that performs the function of both ofsaid tubes at once. Then, in a usual T R apparatus, the periodV 0f timeYthat. elapses. between two signals? mustinot he'v lessv than fthe,de-icnization time of the. tube. this drawback does not eXist'with the,magnetron, sincev the electrons immediately fall on to; the cathodeVwhen the voltage is eliminated; Furthermore, it is possible to apply animpulse ofmuch shorter duration to amagnetron thanthat which is requiredto ionize agas tube, a usual TTR apparatus being unable to operate with4impulsesv of the order of 1/100 of a microsecondxxthat 'can quite wellbe used in a magnetron., Owingfto the nature of the gas, thefprecisionrequiredior the tube andv its shorter life, the ionized tube;,:is lessconvenient tofuse than amagnetromthe-use 'of which does `not linvolveall. these drawbacks...-

In all the examples hereinbefore described,1:it is possible to` use withadvantage a copper mag:`

netron which is provided with cavities andnisV of va special type, withvrounded anodes, so that the anode surfaces.. areYV equi-potentialsurfaces of theV electric eld, such as descrbedlin. the French patentfor Improvements inmagnetrons or like' tubes rintendedfor thetransmission of ultra-short waves, filed by the Compagnie Gen.- er-alede Telegraphie Sans Fil, on April 18, 1947, two consecutive cavities ofVthe magnetron fbeing. in phase opposition, whereby the couplingbetween'rthe cavities is increased.

What we claim is:

.1. An ultra short waveV switching devieecomprising, in combination-z asingle magnetron'having an anode and a. cathode, means for applying;between said anode and. said cathode during f a time t1 a voltage V,vsmaller than the cut-off voltage so as to produce :in the anode-cathodespace of said magnetron a spatial charge ren,- dering the impedance of`this space very small, means for bringing the voltage between cathodeandanode to Zeroduring a time tz consecutivefto t1 so as to eliminatesaidnspa'tialchargexandlto render theimpedance of said space very' high,a rst wave guide connected and coupled laterally to the said Vmagnetronby a first coaxial Yline whose length is approximately equal to arr-oddnumber of quarterwave lengths whereby/the shunt impedance supplied inthis first guide by the magnetron and the said rst coaxialv linefisrenderedver-y strong when the anode ofthe magnetron isat the potential Vand very small when the anode is at the potential zero, so as to makethe said rst guide conductive during the time t1 and non-conductiveduring the time tz, and a second wave guide connected and coupledlaterally to the said single magnetron by a second coaXialAline-Whoselength is approximatelyequal to an integer number of half wave lengthswhereby the shunt impedance supplied in this second guide by themagnetron and the said second coaxial line is, on the contrary, renderedvery small when the anode of the magnetron is at the potential V andvery strong when the anode is at the potential zero so as to make thesaid second guide non-conductive during the time t1 and conductiveduring the time t2.

2. A switching device according to claim 1, wherein the two guides areconnected by one of their ends to a common aerial and by the other end,respectively, to a receiver and to a, pulse transmitter, means beingprovided for synchronizing the periods of the said pulses with theperiods t1 or t2 during which the guide connected to the transmitter isconductive and the guide connected to the receiver, non-conductive.

ANTOINE JEAN ORTUSI. PATRICE FECI-INER.

REFERENCES CITED The following references are of record in the le ofthis patent:

, UNITED STATES PATENTS Number Name Date 2,189,549 Hershberger Feb. 6,1940 2,403,303 Richmond July 2, 1946 2,422,190 Fiske June 17,- 19472,438,367 Keister Mar. 23, 1948 2,483,818 Evans Oct. 4, 1949 2,493,706Washburne et a1. Jan. 3. 1950

